Optical disk having write power adjustment portion

ABSTRACT

An optical disk apparatus adapted to a mark edge recording method having a structure such that a data pattern experimentally recorded on an optical disk with one write power is reproduced plural times while changing reproducing conditions (for example, a slice level for binary-coding a reproduced analog signal) and the number of errors is calculated whenever the reproducing process is performed. The thus-structured process is repeated for using a plurality of write powers. An appropriate write power for the optical disk is determined in accordance with the obtained results of the calculations of the number of errors. In a case of a read-only optical disk, a data pattern experimentally and previously recorded on the optical disk is reproduced plural times by changing the reproducing conditions (for example, a slice level for binary-coding a reproduced analog signal), and the number of errors is calculated whenever the reproducing process is performed. In accordance with the obtained results of the calculations of the number of errors, an appropriate reproducing condition for the optical disk is determined.

This is a divisional of application Ser. No. 09/044,608, filed Mar. 19,1998 now U.S. Pat. No. 5,920,534, which in turn is a divisionalapplication of Ser. No. 08/745,425 filed Nov. 12, 1996 now U.S. Pat. No.5,777,964.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk apparatus.

2. Description of Related Art

An optical disk, such as a photomagnetic disk, is adapted to a datarecording method including a mark pit recording method and a mark edgerecording method. Although the mark pit recording method does notencounter frequent commitment of errors because of direct recording ofthe NRZ code onto the optical disk ("1" indicates existence of a pit and"0" indicates no pit), it suffers from a problem in that the recordingdensity cannot be raised because of a need to electrically distinguishportions "1" from each other in the case where portions "1" are formedsuccessively.

On the other hand, the mark edge recording method is a method in whichthe NRZ code is converted into a code (for example, 1/7 byte code) inwhich portions "1" are not formed successively; and the edge position ofthe pit is made to correspond to "1" or the portion between edges ismade to correspond to "0". The mark edge recording method enables thenumber of "0" to be determined in accordance with the length between "1"and "1". Since the foregoing method is able to raise the recordingdensity by raising the frequency of the operation clocks, the mark edgerecording method is in a trend to be employed in place of the mark pitrecording method.

However, the mark edge recording method involving the structure suchthat the position of each "1" and the length between "1" and "1"correspond to data intended to be recorded and that intended to bereproduced has a necessity of accurately electrically reproducing theedge positions of the recorded pits as well as the necessity ofaccurately reflecting the state of configuration of "1" and "0" of dataintended to be recorded onto the state where data is recorded on themedium.

In a case where the mark edge recording method is performed as shown inFIG. 1 (b) such that the portion of the medium between "1" and "1" issimply irradiated with a laser beam having predetermined power (level1), a formed domain Ds is considerably different from an ideal domainDp, as shown in FIG. 1 (a). Therefore, a pulse train method as shown inFIG. 2 is employed.

With the pulse train method, the level of the write laser output ismaintained at a considerably low assist level (level 0) as shown in FIG.2 (c) when no pit is formed. When pits are formed, the pulses areshifted to have a relatively high level (level 1) (about 2/3 of level 2to be described later) capable of forming pits and a long (a periodwhich is 3/2 of the operation clock shown in FIG. 2 (b)) period. Then,pulses having a higher level (level 2) and a shorter period (a periodwhich is 1/2 of the operation clock) are used to write data. Theabove-mentioned method is able to form the domain Ds having a shapeapproximating the ideal domain Dp as shown in FIG. 2 (a). As a result,the alignment between data intended to be recorded and the domain forrecording data can be maintained.

FIG. 3 is a diagram showing an example of an optical disk apparatusemploying the mark edge recording method. Light reflected from anoptical disk 1 comprising a photomagnetic disk is converted into anelectric signal by a photodetector provided (not shown) for an opticalhead 11. The electric signal obtained by conversion is amplified by anamplifier 12, and then provided with a signal envelope by a low-passfilter 13. Thus, an analog signal as shown in FIG. 4 (a) is obtainedThen, the peak level and the bottom level of the analog signal obtainedfrom a predetermined track (or for a specific time) are confirmed, andthen the obtained value is held in a peak/bottom holder 14. Anintermediate value of the stored values is determined to be a slicelevel L₀.

Then, a binary circuit 15 makes portions higher than the slice level L₀to be "1" and portions lower than the same to be "0", as shown in FIG. 4(b) (that is, the analog signal is binary-coded). Then, as shown inFIGS. 4 (c) and 4 (d), dual data PDATA and NDATA denoting leading edgeand trailing edges are obtained from the foregoing binary signal. Byobtaining the logical sum of the dual data, reproduction data ofrecorded data can be obtained. Then, the obtained signal is, by adecoder 16, decoded to NRZ data required for a usual data process so asto be used.

Although the mark edge recording method is advantageous in realizing ahigh recording density as described above, there arises a necessity thatthe positions of "1" denoted by the recording signals and the intervalsbetween "1" and "1" must be recorded and reproduced to correspond to therecording signals.

In a case where only optical disks of a predetermined type manufacturedby a specific manufacturer are used, the optimum recording conditioncapable of preventing occurrence of errors can definitely be determined.However, the conditions of the optical disk, such as the material andthe thickness of the magnetic film, are somewhat different amongmanufacturers. Therefore, even if the levels (levels 0 to 2) of thelaser beam for use in recording data by the pulse train method are madeto be the same, the state of the formed pits are somewhat different fromone another in the case where the type of the optical disk is different.As a result, the optimum write condition cannot definitely bedetermined.

The pulse train method is required to adjust each of three levels of thelaser beam in order to appropriately record data. Therefore, anappropriate write power must be set and therefore a long time isrequired to set the appropriate write power.

As a method of setting appropriate write power for an optical diskmounted on an optical disk apparatus, a test write method has beenemployed. The foregoing method comprises the steps of test-recordingdata on a predetermined test region of the mounted optical disk with avariety of powers; calculating the number of errors occurring inreproducing recorded data; and an optimum write power is determined inaccordance with a result of the calculation above. However, since thereproducing condition is usually made to be constant in the foregoingprocess, a point, at which the number of errors can satisfactorily bedecreased, cannot be detected precisely. Thus, there arises a problem inthat a satisfactory accuracy cannot be realized in setting theappropriate write power.

A variety of methods of preventing reproduction errors by thereproducing unit have been suggested. For example, a method has beendisclosed in, for example, Japanese Patent Application Laid-Open No.3-91135, in which the amplifying ratio of the amplifying circuit and theamount of delay in the delay circuit are determined optimally inaccordance with the state of reproduction. However, changes in theamplifying ratio and the amount of delay result in change in thereproduction waveform corresponding to FIG. 4 (a). Therefore, a simpleattempt to decrease the number of errors by raising the amplifying ratiocannot be employed. Moreover, adjustment of the two factors, that is,the amount of delay and the amplifying ratio, causes the process to becomplicated excessively.

When the slice level for use in the binary coding process is determinedin the conventional structure, a middle point between the peak level andthe bottom level of analog data reproduced from a specific track isobtained. In the case of data (1/7 data in this case) having domainportions and non-domain portions relatively uniformly distributed asshown in FIGS. 5A and 5B, the above-mentioned method of simply obtainingthe middle point involves slight change in the slice levels La and Lband capability of decreasing the number of errors. However, if a statein which the density of the domain formed portions is high is, as shownin FIG. 5C, rapidly changed to a state in which the density of thedomain formed portions is low, the slice level Lc is sometimes changed.The change in the slice level causes the number of errors to beincreased.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical diskapparatus having a structure such that a process for calculating thenumber of errors by reproducing, under various reproducing conditions, atest pattern recorded with one write power is repeated while changingthe write power so that an appropriate write power for an optical diskis accurately determined.

Another object of the present invention is to provide an optical diskapparatus having a structure such that a test pattern recordedpreviously is reproduced under a variety of reproducing conditions tocalculate the number of errors so that an appropriate reproducingcondition for an optical disk is determined in accordance with theresult of the calculations.

Another object of the present invention is to provide an optical diskapparatus which is capable of setting appropriate write power and/orreproducing condition even if an arbitrary optical disk of a differenttype is loaded so that a disk reproducing state is always maintainedwhile satisfactorily preventing occurrence of an error.

According to one aspect of the present invention, there is provided anoptical disk apparatus, comprising: writing means for writing a specificdata pattern on a predetermined region of an optical disk with variouswrite powers; reproducing means for reproducing the written specificdata pattern; reproducing condition control means for changingreproducing conditions when the specific data pattern written withrespective write powers is reproduced; error number calculating meansfor calculating the number of errors in reproduced data under therespective reproducing conditions; and write power determining means fordetermining an appropriate write power for the optical disk inaccordance with the calculated number of errors. The specific datapattern written on the optical disk with one write power is reproducedplural times while changing the reproducing conditions. Whenever thereproduction process is performed, the number of errors is calculated.The foregoing process is repeated with the plural write powers. Inaccordance with the result of the calculations of the number of errors,the appropriate write power for the optical disk is determined.

According to another aspect of the present invention, there is providedan optical disk apparatus, comprising: reproducing means for reproducinga specific data pattern written on an optical disk; reproducingcondition control means for changing reproducing conditions when thespecific data pattern is reproduced; error number calculating means forcalculating the number of errors in reproduced data under the respectivereproducing conditions; and reproducing condition determining means fordetermining an appropriate reproducing condition for the optical disk inaccordance with the calculated number of errors. The specific datapattern, which has been previously written, is reproduced plural timeswhile changing the reproducing conditions. Whenever the reproductionprocess is performed, the number of errors is calculated. In accordancewith the result of the calculations of the number of errors, theappropriate reproducing condition is determined.

The reproducing conditions which are changed consist of a slice levelfor use when an analog signal supplied from the optical disk isbinary-coded, Window Tap which is the phase difference between theanalog signal supplied from the optical disk and a prepared referenceclock and a boost value of an electronic filter of the reproducingmeans.

When, for example, the slice level is changed, a plurality of offsetvalues are provided for a predetermined slice level when the specificdata pattern is reproduced so as to change the slice level. Then, thenumber of errors in reproduced data is calculated at each slice level sothat the total number of errors is obtained. In accordance with thetotal number of errors at the respective reproducing conditions, theappropriate write power and/or the appropriate reproducing condition aredetermined.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a record domain of an optical disk;

FIG. 2 is a diagram showing a record domain of the optical disk;

FIG. 3 is a diagram showing an example of the structure of aconventional optical disk apparatus;

FIG. 4 is a graph showing waveforms in the units shown in FIG. 3;

FIGS. 5A to 5C are diagrams showing the relationship among an NRZsignal, a 1/7 byte signal, a record pattern and a reproduced analogsignal;

FIG. 6 is a block diagram showing the principle of an optical diskapparatus according to a first embodiment of the present invention;

FIG. 7 is a diagram showing an example of the structure of the opticaldisk apparatus according to the first embodiment of the presentinvention;

FIGS. 8A, 8B are flow charts showing the operation procedure of theoptical disk apparatus according to the first embodiment of the presentinvention;

FIG. 9 is a graph showing the relationship between the reproduced analogsignal and a slice level;

FIG. 10 is a graph showing the relationship between the number of errorsand the slice level;

FIG. 11 is a block diagram showing the principle of an optical diskapparatus according to a second embodiment of the present invention;

FIG. 12 is a diagram showing an example of the structure of the opticaldisk apparatus according to the second embodiment of the presentinvention;

FIGS. 13A, 13B are flow charts showing the operation procedure of theoptical disk apparatus according to the second embodiment of the presentinvention; and

FIG. 14 is a diagram showing a format of the optical disk according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the drawings.

First Embodiment

An optical disk apparatus according to a first embodiment of the presentinvention will now be described in which an appropriate write power canbe set for an optical disk. FIG. 6 is a block diagram showing theprinciple and structure of the first embodiment which is capable ofobtaining an optimum write power. When an optical disk has been loadedonto an optical disk apparatus, a write control means 40 experimentallyrecords a specific data pattern in a predetermined region of the opticaldisk with a certain write power. The recorded specific data pattern isread by a reproducing means 10. At this time, a reproducing conditioncontrol means 50 changes the reproducing condition in the reproducingmeans 10 so that one specific data pattern is read under a variety ofreproducing conditions. Specifically, the following reproducingconditions are changed which include the slice level for use in theoperation for binary-coding an analog signal from the optical disk;Window Tap which is the phase difference between the analog signalsupplied from the optical disk and a prepared reference clock; and theboost value of an electronic filter (not shown) of the reproducing means10. The number of errors occurring in the reproduced signal read underthe respective reproducing conditions is calculated by a error-numbercalculating means 30. The result of the calculations is transmitted toan optimum write power determining means 20.

After the data pattern recorded with one write power under all of thereproducing conditions has been reproduced, the write control means 40again records the data pattern for test with another write power. Alsothis data pattern is reproduced under a variety of reproducingconditions so that result of calculations in the respective reproducingconditions is obtained.

Then, the data pattern for test is recorded with still another writepower to obtain result of calculations by a similar method. Theforegoing process is repeated plural times. Finally, the optimum writepower is determined in accordance with results of the calculations ofthe number of errors supplied to the optimum write power determiningmeans 20.

FIG. 7 is a diagram showing an example of the structure of the firstembodiment. FIGS. 8A, 8B are flow charts showing the operation procedureof the first embodiment.

When the power source is turned on, an initial setting means 80 of anMPU 200 is operated so that default values which are originallysupported by the optical disk apparatus, such as the amplifying ratio ofan amplifier 12 with respect to an optical disk 1 and the transmissivefrequency of a low-pass filter 13, are set. As a matter of course,default values of the recording system, such as three levels consistingof assist level, level 1 and level 2 shown in FIG. 2 and the like are,together with changes of power tables of MO (Magneto Optical) and DOW(Direct Over Write), set, as well as those of the reproducing system(step S1).

Then, the write control means 40 is operated so that a specific patternstored in a test pattern memory 90 is written on a predetermined regionof the optical disk 1 (step S2). Write conditions at the foregoing writeprocess, such as the assist level, level 1 and level 2 (see FIG. 2), arethe default values. At this time, a pattern as shown in FIG. 5C withwhich a highest possible error occurrence rate can be realized iswritten.

After the foregoing write process has been completed, a read controlmeans 70 is operated so that the reproducing laser of an optical head 11is turned on. Thus, the written test pattern is reproduced. Lightreflected by the optical disk 1 is, by a photodetector (not shown)provided for the optical head 11, converted into an electric signal. Theelectric signal obtained by the conversion above is amplified by anamplifier 12, and then allowed to pass through a low-pass filter 13 andan electronic filter 17 so that an analog reproduced signal as shown inFIG. 4 (a) is obtained. The peak and bottom levels of the analog signalare held in a peak/bottom holder 14. The analog signal is binary-codedby a binary circuit 15 with a slice level which is an intermediate valuebetween the peak level and the bottom level so that a binary signal asshown in FIG. 4 (b) is obtained. Dual data PDATA and NDATA denoting theleading and trailing edges of the binary signal and forms as shown inFIGS. 4 (c) and 4 (d) are obtained from the binary signal above. Byobtaining the logical sum of the dual data items, reproduced data ofrecorded data can be obtained. Then, the thus-obtained signal is, by adecoder 16, decoded into NRZ data which is required by a usual dataprocess.

When the foregoing reproducing process is performed, the reproducingcondition control means 50 of the MPU 200 is operated so that the slicelevel obtained in the binary process is supplied to the binary circuit15. With the supplied slice level, data is reproduced (step S3). Inaccordance with the thus-obtained binary signal, the signal is convertedinto NRZ data by the decoder 16. The error-number calculating means 30calculates the number of errors in the output from the decoder 16 andstores the result of calculation into a register 60 (step S4).

The error-number calculating means 30 has an ECC (ErrorChecking/Correction) circuit 32 and a data comparison circuit 33 whichare circuits for calculating the number of errors. The error-numbercalculating means 30 controls switches 31 and 34 to select the circuitfor use to calculate the number of errors. The data comparison circuit33 compares the output from the decoder 16 and the test patternpreviously stored in the test pattern memory 90 to each other so as tocalculate the number of errors. The data comparison circuit 33 is ableto detect the bit encountered an error in addition to detecting thenumber of errors. However, the ECC circuit 32 is able to only detect thenumber of errors. In the case where only the number of errors isrequired to be detected, the ECC circuit 32 has a higher processingspeed than that of the data comparison circuit 33.

Then, the reproducing condition control means 50 changes the slice leveland the number of errors is calculated by similarly reproducing the testpattern. The result of calculation is stored into the register 60 so asto be added to the previous result of calculation. Then, a similarprocess (reproduction of the test pattern, calculation of the number oferrors, and storage and addition of the results of the calculations) isperformed for all of the slice levels (steps S3, S4 and S5 are repeated)in such a manner that the slice level is changed.

After reproduction of all slice levels has been completed (step S5:YES), the reproducing condition control means 50 is operated to changeWindow Tap and reproduce the test pattern (step S6). Also in this case,the ECC circuit 32 or the data comparison circuit 33 in the error-numbercalculating means 30 is operated to calculate the number of errors andthe result of calculation is stored into the register 60 (step S7). TheWindow Tap is further changed to similarly reproduce the test pattern soas to calculate the number of errors. The result of calculation isstored into the register 60 and then added to the previous result ofcalculation. Then, while changing the Window Tap, a similar process(reproduction of the test pattern, calculation of the number of errors,and storage and addition of the results of the calculations) isperformed for all of the Window Tap (steps S6, S7 and S8 are repeated).

After reproduction for all Window Tap has been completed (step S8: YES),the reproducing condition control means 50 is operated so that the boostvalue of the electronic filter 17 is changed to reproduce the testpattern (step S9). Also in this case, the ECC circuit 32 or the datacomparison circuit 33 in the error-number calculating means 30 isoperated to calculate the number of errors, and the result ofcalculation is stored into the register 60 (step S10). The boost valueis further changed to similarly reproduce the test pattern so as tocalculate the number of errors. The result of calculation is stored intothe register 60 and added to the previous result of calculation. Then,while changing the boost value, a similar process (reproduction of thetest pattern, calculation of the number of errors, and storage andaddition of the results of the calculations) is performed for all boostvalues (steps S9, S10 and S11 are repeated).

After the foregoing sequential reproducing processes for the testpattern recorded with certain write power under all of the reproducingconditions have been completed (step S11: YES:), whether processes ofthe test pattern with all of the write powers have been completed isdetermined (step S12).

If the processes have not been completed, signal denoting this istransmitted from the read control means 70 to the write control means 40so that the write control means 40 is operated and the write power ischanged to a level different from that in the previous process (stepS13). Then, the specific pattern stored in the test pattern memory 90 isagain written on a predetermined region of the optical disk 1 (step S2).Then, the foregoing test pattern is subjected to a similar reproductionprocess (steps S3 to S11).

A sequence of processes of the test pattern recorded with all of thewrite powers (for example, five kinds of powers) has been completed(step S12: YES), the optimum write power determining means 20 reads theadded number of errors stored in the register 60 and determines thewrite power with which the smallest added value is obtained as optimumwrite power (step S14).

A case will now be considered in which the slice level is changed. Theresult is obtained such that number of errors at a plurality of slicelevels with one write power is obtained, that is, the total number oferrors is large with certain write power and the total number of errorsis small with another write power level. It can be said that the writepower with which the number of errors is not changed considerably if theslice level is changed is an appropriate level and that the write powerwith which the number of errors deteriorates if the slice level ischanged slightly is unsatisfactory. Therefore, the total number oferrors at a plurality of slice levels can be employed as an index whenappropriate write power is determined.

Although the procedure for changing the three reproducing conditionincluding the slice level, Window Tap and the boost value has beendescribed in the foregoing embodiment, only one or two reproducingconditions may, of course, be changed.

Although the sequential reproduing process is performed with a pluralityof write powers, appropriate write power can be determined if a testpattern recorded with one write power is subjected to a similar process.Since the first embodiment enables the result of the calculations of thenumber of errors with one write power to be obtained, considerablyappropriate write power can be determined in accordance with the resultof the calculations and the one write power.

As described above, the first embodiment has the structure such that atest pattern recorded with one write power or plural write powers issubjected to the reproducing process under the plural reproducingconditions. Therefore, appropriate write power for an arbitrary opticaldisk can accurately be set. As a result, the recording and reproducingoperations of an optical disk apparatus adapted to the mark edgerecording method requiring appropriate and accurate write power canaccurately be performed.

Second Embodiment

An optical disk apparatus according to a second embodiment of thepresent invention which is capable of setting an appropriate reproducingcondition for an optical disk will now be described. A structure forsetting an appropriate slice level for a binary-coding process withrespect to an optical disk will now be described in which a slice levelfor use in binary-coding an analog signal obtained from the optical diskis employed as the reproducing condition which is changed when a testpattern is reproduced.

In general, the number of errors occurring when a analog reproducedsignal supplied from an optical disk is, as shown in FIG. 9, sliced withlevels A, B, C, D and E forms a parabola as shown in FIG. 10. It isideal to determine the slice level at the leading end of the parabola insuch a manner that the number of errors is smaller than 10⁻⁶. The idealslice level does not always coincide with the middle point of the peaklevel and the bottom level of the reproduced signal. Therefore, optimumslice level C must be realized by adding offset of correction value V₀when the middle point between the peak level and the bottom level is P₀.

FIG. 11 is a block diagram showing the principle and structure of asecond embodiment for obtaining the optimum slice level C. The binarycircuit 15 of the reproducing means 10 is supplied with an analogreproduced signal and the middle point between the peak level and thebottom level of the analog reproduced signal, the middle point beingsupplied as the slice level. A slice level changing means 120 supplies,to the binary circuit 15, an offset value for changing the slice levelinto a plurality of levels. The plural slice levels are used to read apredetermined specific pattern of the optical disk.

The error-number calculating means 30 calculates the number of errors inthe reproduced and demodulated signal read with each slice level. Aslice level correcting means 130 obtains upper and lower limits of theslice level with which the number of errors is made to be smaller thanan allowable value in accordance with the calculated number of errors,and then determines the middle point of the upper and lower limits to bethe optimum slice level. When the optimum slice level has beendetermined, a correction value (an offset value) for the slice level(the middle point between the peak level and the bottom level) suppliedfrom the peak/bottom holder 14 corresponding to the optimum slice levelcan be determined. The offset value is supplied to the binary circuit15.

When margin of the upper and lower limits of the slice level with whichthe number of errors is made to be smaller than an allowable value arewide, the optimum slice level can easily be determined by narrowing themargin. Therefore, the reproducing condition control means 50 changesthe transmissive frequency of a low-pass filter (not shown) of thereproducing means 10 and/or the boost value of an electronic filter (notshown) of the reproducing means 10 is changed to intentionally form areproduced signal having a large number of errors. Then, the margin isnarrowed so that the optimum slice level is easily determined.

FIG. 12 is a diagram showing an example of the structure of the secondembodiment. FIGS. 13A, 13B are flow charts showing the operation of thesecond embodiment. Referring to FIG. 12, elements given the samereference numerals are similar elements. Also the error-numbercalculating means 30 according to the second embodiment shown in FIG. 12has the ECC circuit 32, the data comparison circuit 33 and switches 31and 34 shown in FIG. 7.

When the power source is turned on, the initial setting means 80 of theMPU 200 is operated so that default values, such as the amplifying ratioof the amplifier 12 corresponding to the optical disk 1 originallyadapted to the optical disk apparatus and the transmissive frequency ofthe low-pass filter 13 and the like, are set. As a matter of course,default values of the recording system, as well as those of thereproducing system, such as three levels consisting of assist level,level 1 and level 2 shown in FIG. 2 and the like are set (step S21).

When the optical disk 1 has been loaded onto the optical disk apparatus,a medium judging means 110 determines whether the loaded optical disk isan optical disk supported by the optical disk apparatus (step S22). Ifthe optical disk apparatus supports the optical disk 1 (step S22: YES)and the optical disk 1 is a disk, the default values of which have beenset in step S21 (step S31: YES), recording and reproducing are performedin accordance with the set default values.

In a case where the optical disk is not supported, the write controlmeans 40 is operated so that a specific pattern stored in the testpattern memory 90 is written on a predetermined region of the opticaldisk 1 (step S23). Write conditions, such as the assist level, level 1,level 2 (see FIG. 2) and the like for use in the write operation are thedefault values. At this time, a pattern having the highest possibleerror commitment ratio as shown in FIG. 5C is written.

After the foregoing write operation has been completed, a reproductioncontrol means (not shown) is operated so that the reproducing laser ofthe optical head 11 is turned on so that the written test pattern isreproduced. The operation of each circuit in the reproducing means 10 isperformed similarly to those of the first embodiment so that a middlepoint between the peak level and the bottom level of the analogreproduced signal is supplied from the peak/bottom holder 14 to thebinary circuit 15 as the slice level.

When the foregoing reproducing operation is performed, the slice levelchanging means 120 of the MPU 200 is operated so that an offset valuefor making the slice level supplied from the peak/bottom holder 14 tobe, for example, level A shown in FIG. 9 is supplied to the binarycircuit 15. Then, reproduction is performed with the slice level A (stepS24). The thus-obtained binary signal is converted into dual data shownin FIGS. 4 (c) and 4 (d), and then, by the decoder 16, converted intoNRZ data required to perform an information process.

The error-number calculating means 30, similarly to the firstembodiment, calculates the number of errors Era in accordance with anoutput from the decoder 16, and then stores, together with the slicelevel A, the result of the calculation into a register Ra (step S25).Then, slice level B higher than the level A is used to calculate thenumber of errors Erb which is stored into a register Rb. As describedabove, while sequentially raising the slice level as A→B→C→D→E, thenumbers of erros Era, Erb, Erc, Erd and Ere with the corresponding slicelevels are sequentially stored into registers Ra, Rb, Rc, Rd and Re(steps S24, S25 and S26 are repeated in this sequential order).

Then, the slice level correcting means 130 compares the number of errorsstored in the registers Ra to Re with one another to determine upper andlower limits of the slice level with which the number of errors is madeto be a value smaller than an allowable value (step S27). Then, theslice level correcting means 130 determines whether the margin betweenthe determined upper and lower limits is larger than a predeterminedvalue (step S28).

If the margin is not larger than the predetermined value, anintermediate level between the upper and lower limits is set to be theoptimum slice level, and then a correction value for making the slicelevel (a middle point between the peak level and the bottom level)transmitted from the peak/bottom holder 14 to be the optimum slice levelis, as the offset value, stored into an offset value memory 140 (stepS29). As a result, the optimum slice level can be obtained. Thus,reproduction is always performed with the slice level obtained bysetting off the slice level (the middle point between the peak level andthe bottom level) transmitted from the peak/bottom holder 14 with theforegoing correction value when following usual reproduction operationsare performed.

If the margin is larger than the predetermined value in step S28, thereproducing condition is changed to widen the margin (step S30). Even ifa pattern causing the error commitment ratio to be raised is used, theactual number of errors is made to be different depending upon the typeof the medium. Therefore, in a case of a curve shown in FIG. 10, themargin (refer to V₁ shown in FIG. 10) between the upper and lower limitsof the slice level is different depending upon the medium. If the marginis wide, the curve is made to be too gentle to easily determine thecentral level. Therefore, if the margin is too wide, the reproducingcondition control means 50 may make the set value of, for example, theelectronic filter 17 to be variable so as to change the boost value andso as to change the transmissive frequency for the low-pass filter 13 inplace of changing the boost value of the electronic filter 17.

When the slice level and the other read conditions for an optical diskof a specific type have been determined, these conditions are, togetherwith the type of the optical disk, stored into the storage means so asto be used as the judging conditions for use by the medium judging means110. If the optimum slice level has been determined because of aprevious experimental write (step S22: YES) and the optical disk is notan optical disk, the default values of which have not been set (stepS31: NO), the default values written in step S21 are rewritten (stepS32). Then, a usual process is performed.

If the foregoing calculation of the number of errors and thedetermination of the correction value (the offset value) are performedin accordance with calculation of number of errors performed pluraltimes, more accurate reproduction can be performed. Although the optimumslice level is made to be an intermediate value between the upper andlower limits of the slice level which is lower than an allowable level,the changing pitch to the slice level by the slice level changing means120 may be more reduced to obtain the slice level corresponding to thesmallest number of errors indicated by the curve shown in FIG. 10.

As described above, the second embodiment has the structure such thatthe slice level with respect to the analog reproduced signal isdetermined by correcting the middle point between the peak level and thebottom level of the reproduced signal in such a manner that the numberof errors is made to be smallest when an optical disk is reproduced.Moreover, the determination of the slice level is performed for eachtype of the optical disk. As a result, even if an optical disk of adifferent type is used, reproduction can always be performed in such amanner that errors commitment can be prevented satisfactorily.

Although the foregoing embodiment has been structured such that thenumber of errors is calculated while changing the slice level when thetest pattern is reproduced, the reproducing condition for the change maybe similar to the first embodiment in which Window Tap or the boostvalue of the electronic filter are changed as well as the slice level.Although the description has been performed about determination of anappropriate slice level for use in the binary-coding process which isperformed when reproduction is performed, the foregoing structure is anexample. As a matter of course, another appropriate reproducingconditions such as appropriate read power to be employed in thereproduction process, can be determined similarly.

Although the foregoing embodiment has the structure such that thespecific test pattern is temporarily written on a predetermined regionof the optical disk 1, the foregoing process for determining theappropriate reproducing condition may be performed for a read-onlyoptical disk. In the foregoing case, a specific data pattern ispreviously recorded in the test write region of the read-only opticaldisk. FIG. 14 is a diagram showing a record format of the read-onlyoptical disk for one zone in which a test write region having a specifictest pattern recorded previously is provided in the rear of pluralsectors consisting of an ID region and a data region.

Although the first embodiment may be structured such that the slicelevel changing means 120 and the offset value memory 140 are providedsimilarly to the second embodiment so as to provide a plurality ofoffset values for a predetermined slice level in order to set pluralslice levels.

Although the first embodiment has the structure such that judgmentwhether a loaded optical disk is a supported optical disk is notperformed when the optical disk has been loaded, the medium judgingmeans 110 may be provided similarly to the second embodiment to performthe process (steps S22, S31 and S32 shown in FIG. 13A) for judgingwhether the loaded optical disk is supported or not.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims or equivalence of such metes and bounds thereofare therefore intended to be embraced by the claims.

What is claimed is:
 1. An optical disk, comprising:a test region used tooptimize a write power level used to record data and a slice level usedto reproduce data; wherein a specific data pattern is recorded at pluralwrite power levels in said test region and after each time said specificdata pattern is recorded, said specific data pattern is reproducedplural times using different offset values and a number of errors isdetermined for each offset value; wherein an optimum combination ofwrite power level and offset value is determined among pluralcombinations each of which consists of a selected one of said pluralwrite power levels and a selected one of said offset values, saidoptimum combination yielding a lowest number of errors duringreproduction; wherein said specific data pattern comprises domainportions and non-domain portions both uniformly distributed.
 2. Anoptical disk, comprising:a test region used to optimize a write powerlevel used to record data and a slice level used to reproduce data;wherein a specific data pattern is recorded at plural write power levelsin said test region and after each time said specific data pattern isrecorded, said specific data pattern is reproduced plural times usingdifferent slice levels and a number of errors is determined for eachslice level; wherein an optimum combination of write power level andslice level is determined among plural combinations each of whichconsists of a selected one of said plural write power levels and aselected one of said slice levels, said optimum combination yielding alowest number of errors during reproduction; and wherein the specificdata pattern comprises domain portions and non-domain portions bothuniformly distributed.
 3. An optical disk, comprising:a test region usedto optimize a write power level used to record data and a slice levelused to reproduce data; wherein a specific data pattern is recorded atplural write power levels in said test region and after each time saidspecific data pattern is recorded, said specific data pattern isreproduced plural times using different offset values and a number oferrors is determined for each offset value; wherein an optimumcombination of write power level and offset value is determined amongplural combinations each of which consists of a selected one of saidplural write power levels and a selected one of said offset values, saidoptimum combination yielding a lowest number of errors duringreproduction; wherein the specific data pattern comprises a domainportion whose forming density changes rapidly from a high degree to alow degree or vice versa.
 4. An optical disk, comprising:a test regionused to optimize a write power level used to record data and a slicelevel used to reproduce data; wherein a specific data pattern isrecorded at plural write power levels in said test region and after eachtime said specific data pattern is recorded, said specific data patternis reproduced plural times using different slice levels and a number oferrors is determined for each slice level; wherein an optimumcombination of write power level and slice level is determined amongplural combinations each of which consists of a selected one of saidplural write power levels and a selected one of said slice levels, saidoptimum combination yielding a lowest number of errors duringreproduction; and wherein the specific data pattern comprises a domainportion whose forming density changes rapidly from a high degree to alow degree or vice versa.